1. Technical Field
The present invention relates to a light emitting device using a light emitting material such as an organic EL (Electroluminescent) material, a driving method thereof, and an image forming apparatus using the light emitting device.
2. Related Art
A printer as an image forming apparatus uses a light emitting device in which a plurality of light emitting elements are arranged in an array form as a head unit that forms an electrostatic latent image on an image carrier such as a photosensitive drum or the like. The head unit is generally constructed with a plurality of light emitting elements disposed in a single line along a main scanning direction.
A well-known light emitting element is an organic light emitting diode (hereinafter referred as OLED). In the light emitting element such as an OLED element, light emission intensity in particular, luminosity, changes according to the magnitude of a driving current. As a method of driving the OLED element, a PWM (pulse width modulation) method, in which a pulse width of a driving current to be supplied to the OLED element is regulated based on gradation, has been disclosed in JP-A-2004-330472 (see claim 10).
However, it is difficult to form a plurality of OLED elements in a uniform manner in an actual head unit. Accordingly, even when a driving current having a certain magnitude is respectively supplied to the plurality of OLED elements for the same period of time, the light emission intensity varies.